Clay-carbon composites and the carbons derived from demineralization of the clay template were examined for their aqueous adsorption properties (2,4,6-trichlorophenol and methylene blue) and for their gas adsorption/separation abilities regarding CO2, CH4, and N-2 gases. The sorption results are discussed in relation with their structural properties (surface area, pore width and volume, and surface chemistry). It was found that the properties of the adsorbents depend highly on the synthetic route, for instance, on the use of clay or H2SO4 as structure mediating and activating agents, respectively. Particularly, the simultaneous use of clay and H2SO4 leads to a synergistic action, which imparts to the final solids the highest sorption capacity and the best potential for separation of CO2 from gaseous mixtures of CH4 and N-2.